Help needed in segmentation fault

babycorn · 02-15-2006, 11:16 AM

Hi! I am facing problems here... This is the coding that i compile in linux terminal :
#include <stdio.h>
void *mymalloc(size_t request);
int main()
{
char * test;
int i = 0;
test = (char *)mymalloc(sizeof(char) * 6);
if (test == NULL)
{
printf("Malloc failed\n");
exit(1);
}
while(1)
{
test[i] = 'a';
printf("%d bytes written to memory\n", i+1);
i++;
}
return 0;
}
void * mymalloc(size_t request)
{
return sbrk(request);
}

and this is my output:
2565 bytes written to memory
2566 bytes written to memory
2567 bytes written to memory
2568 bytes written to memory
Segmentation fault

Can anyone explain to me what's actually happenning? If want to improve, how?? Thanks a lot for your help!!!

dmail · 02-15-2006, 11:48 AM

Code:

while(1)
{
test[i] = 'a';
printf("%d bytes written to memory\n", i+1);
i++;
}

This infinite loop is what is causing the seg fault, but I've never seen the sbrk func?

Matir · 02-15-2006, 12:22 PM

You're definitely overflowing your buffer by a long shot... you allocate a 6 byte buffer and then dump several hundred bytes into it.

xhi · 02-15-2006, 12:43 PM

change

Code:

while(1)

to

Code:

while(i<6)

and please use code tags

edit> also according to the man page sbrk is not defd in c standard..